This invention relates generally to a gas generation system and, more particularly, to a gas generator utilizing liquid monopropellants, such as hydroxyl ammonium nitrate based liquid monopropellants and the like, as a combined oxidizer/fuel source where the generator may have a constant-output or a variable-output, depending on its intended application.
Over the past several decades there has been strong interest in liquid propellant technology, generally for use in propelling munitions. For example, U.S. Pat. No. 4,745,841, entitled "Liquid Propellant Gun", to Magoon et al, teaches a propellant gun wherein the mass rate of flow of liquid propellant can be repetitively, selectively and continuously varied throughout the interval of time of firing a single shot. This patent and all references cited therein are hereby incorporated in their entirety by reference. There are a number of energetic liquids which could be used for propelling munitions. For example, hydrazine and hydrogen peroxide are readily available. Hydrazine, however, is extremely toxic and requires stringent safeguards for human safety, while hydrogen peroxide, in concentrations of practical interest, is inherently unstable and is a severe fire hazard.
Liquid propellants are useful because copious amounts of gas are generated as the propellants burn and propel the munitions out from the gun barrel. Although large amounts of gas are produced, the reaction is an extremely short lived phenomenon, i.e., on the order of 10-20 milliseconds, and therefore liquid propellants have been heretofore limited in their applications. However, some applications need a substantial volume of gas delivered at a specified pressure over a given length of time, such as for the starting of rotating machinery (e.g., diesel engines and gas turbines), inflation of gas bags (e.g., deep sea salvage inflation devices and automotive air bags), and steady-state operation of turbine-driven machinery.
There are currently other methods available for such applications, but these other methods present undesirable properties. Charged flasks of high pressure gas, for example, can be stored and used to initiate rotation of diesel engines, but these flasks are very bulky, have a finite pressure life and require a heavy and complex compressor for recharging. Another method is to combust gases to generate a subsequent high-temperature gas which fills the flasks. However this method is almost never used for this purpose because of the bulk associated with housing large amounts of gas and the safety of carrying a flammable gas. By far, the most prevalent energy source for voluminous gas generation involves the combustion of solid propellants. Although solid propellants are simple, and produce large amounts of gas, such propellant systems lack flexibility, must be replaced after each use, and their combustion products frequently contain undesirable components. Also, once the ignition process is started, it typically cannot be stopped until all of the propellant is consumed. Systems employing liquids, on the other hand, are quite flexible in that they can be readily started, throttled, stopped, and refilled after use.